Extracorporeal shock wave therapy (ESWT) represents a potentially important treatment modality for plantar fasciitis, lateral epicondylitis, shoulder tendonitis, non-unions, and other areas in orthopedics. ESWT is also an alternative to surgery for patients who do not respond well to conservative treatments. However, there is no consensus on the mechanism of action, nor is there any understanding of how musculoskeletal structures affect energy propagation. This proposal examines the basic effects of shock wave (SW) propagation through musculoskeletal structures. The specific roles of cavitation and shear will be quantified and used to optimize ESWT protocols. Specific recommendations to orthopedic physicians on how best to use current technology will be a major goal of this research. We have three specific aims. The first is to quantify SW propagation through musculoskeletal structures. We will use state-of-the-art finite volume techniques to predict how musculoskeletal structures impede and deflect acoustic energy propagation. The modeling effort will lead to predictions of shear stress and cavitation behavior. Our other two aims are to experimentally quantify cavitation and shear waves. These studies will be used to validate the modeling effort, and to serve as vectors for directing the modeling effort. Cavitation will be measured using acoustic detectors (passive cavitation detectors, B-mode ultrasound). Shear waves will be measured using polarization optics and transparent bone models. This effort is relevant to the public health because currently, shock wave therapy is being used to treat a variety of conditions, such as heel pain, elbow pain, shoulder pain, and hip pain. However, there is no research into how the shock waves actually cause the body to repair itself. By understanding the basic science of shock wave interaction with bones and tissues, we will be able to provide recommendations to physicians on how to optimize their treatments of these conditions.